Thermal conditioning fluids for an underwater cryogenic storage vessel

ABSTRACT

Technologies are described herein for conditioning fluids stored in an underwater cryogenic storage vessel designed for use in a fuel system of an underwater vehicle. According to one aspect of the disclosure, a fuel system includes a fuel cell and a storage vessel, which stores a first fluid that is supplied to the fuel cell and a second fluid that is produced by the fuel cell. The fuel system also includes a thermal conditioning module that receives the first fluid from the storage vessel and receives the second fluid from the fuel cell. The first fluid stored in the storage vessel is conditioned by absorbing heat from the second fluid, such that the fuel cell receives the conditioned first fluid. The second fluid received from the fuel cell is in gaseous state and is converted to a liquid. The liquid second fluid is stored in the storage vessel.

CROSS-REFERENCE OF RELATED APPLICATIONS

This application is a division of co-pending U.S. application Ser. No.12/552,136, filed on Sep. 1, 2009, entitled, “Thermal ConditioningFluids For An Underwater Cryogenic Storage Vessel”, which is related toU.S. application Ser. No. 14/162,188, filed on Jan. 23, 2014, entitled“Underwater Cryogenic Storage Vessel and Method of Using Same,” and isalso related to U.S. Pat. No. 8,651,313, issued on Feb. 18, 2014,entitled, “Underwater Cryogenic Storage Vessel”, which is expresslyincorporated herein by reference in its entirety.

GOVERNMENT RIGHTS

This invention was made with Government support under contract numberHR0011-06-C-0073 awarded by the United States Navy. The government hascertain rights in this invention.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to fuel systems, and inparticular to thermal conditioning cryogenic fluids associated with fuelsystems for underwater vehicles.

BACKGROUND

Some vehicles, such as underwater vehicles, have a fuel system that usesa fuel cell to provide power to the vehicle. Typically, these fuel cellsare supplied with kerosene and oxygen to produce power. These fuel cellsalso produce carbon dioxide as an effluent. In such power systems, theoxygen supplied to the fuel cell is stored in storage tanks, which areconnected to the fuel cell. The resulting carbon dioxide is collectedand stored in separate storage tanks.

In existing power systems of such vehicles, the oxygen is stored as aliquid in storage tanks arranged adjacent to each other. Beforesupplying the oxygen to the fuel cell, the liquid oxygen in these tanksmay need to be boiled off, such that the oxygen supplied to the fuelcell is in a gaseous state. However, the heat supplied to one of thetanks for boiling off the oxygen may dissipate to the other tanks in thevicinity, thereby increasing the temperature and consequently, thepressure in the storage tanks adjacent to the tank that is beingsupplied with heat.

In an attempt to reduce the effect of the dissipated heat on the othertanks located in the vicinity, the tanks are conventionally made withinsulated vacuum gaps to reduce the amount of heat that may leak intothe unused tanks. However, because of the insulated gaps, these tankstake up a larger volume. Further, because there may still be some heatleak into the storage tanks despite the insulated gaps around thestorage tanks, the fluids in the tanks may expand due to an increase inpressure. In order to account for the possibility of fluid expansion,these conventional tanks are typically only partially-filled, therebyrequiring tanks with greater volume to store the amount of fuel desired.

It is with respect to these and other considerations that the disclosuremade herein is presented.

SUMMARY

Technologies are described herein for thermal conditioning fluidsassociated with a fuel system. According to one aspect of thedisclosure, a fuel system includes a fuel cell and a storage vessel. Thestorage vessel is configured to store a first fluid that is supplied tothe fuel cell and a second fluid that is supplied by the fuel cell. Thefirst fluid includes a liquid first fluid and a gaseous first fluid, andthe second fluid includes a liquid second fluid and a gaseous secondfluid. The fuel system also includes a thermal conditioning module thatis configured to receive the gaseous first fluid from the storage vesseland also to receive the gaseous second fluid from the fuel cell. Thegaseous first fluid stored in the storage vessel is conditioned byabsorbing heat from the gaseous second fluid, such that the fuel cellreceives the gaseous first fluid from the thermal conditioning module.The gaseous second fluid received from the fuel cell is converted to theliquid second fluid. The liquid second fluid is then stored in thestorage vessel.

In another aspect of the present disclosure, a fuel system includes athermal conditioning module. The thermal conditioning module isconfigured to receive a gaseous first fluid from a storage vessel and agaseous second fluid from a fuel cell. The gaseous first fluid from thestorage vessel is conditioned by absorbing heat from the gaseous secondfluid to create a conditioned gaseous first fluid. A first portion ofthe conditioned gaseous first fluid is provided to the fuel cell, whilea second portion is provided back to the storage vessel. The gaseoussecond fluid from the fuel cell is converted to a liquid second fluidand provided to the storage vessel.

In yet another aspect, a fuel system includes a fuel cell, a storagevessel, and a thermal conditioning module. The storage vessel includestwo storage tanks, each configured to store a first fluid to be suppliedto the fuel cell. The storage vessel also includes a storage compartmentconfigured to store a liquid second fluid supplied by the fuel cell. Thethermal conditioning module receives the first fluid from the storagevessel and receives a gaseous second fluid from the fuel cell. The firstfluid is conditioned by absorbing heat from the gaseous second fluidfrom the fuel cell to create a conditioned first fluid. A portion of theconditioned first fluid is provided to the fuel cell and a secondportion is provided back to the storage vessel. The gaseous second fluidfrom the fuel cell is converted to a liquid second fluid and provided tothe storage compartment for storage.

It should be appreciated that the above-described subject matter mayalso be implemented in various other embodiments without departing fromthe spirit of the disclosure. These and various other features will beapparent from a reading of the following Detailed Description and areview of the associated drawings.

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intendedthat this Summary be used to limit the scope of the claimed subjectmatter. Furthermore, the claimed subject matter is not limited toimplementations that solve any or all disadvantages noted in any part ofthis disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating a fuel system comprising a fuelcell, a thermal conditioning module, and a storage vessel, according toembodiments described herein;

FIG. 2 is a cut-open view of the storage vessel, according toembodiments described herein;

FIG. 3 is a partial cut-open view and partial bottom view of the storagevessel, according to embodiments described herein;

FIG. 4 is a line diagram illustrating the flow of fluids within thestorage vessel, according to embodiments described herein;

FIG. 5 is a block diagram illustrating a thermal conditioning module ofa fuel system, according to embodiments described herein;

FIG. 6 is a logical flow diagram illustrating a routine for operatingthe fuel system, according to embodiments described herein;

FIG. 7 is a logical flow diagram illustrating a routine for storing aneffluent in a storage tank of the storage vessel, according toembodiments described herein; and

FIG. 8 is a logical flow diagram illustrating a routine for conditioningthe storage tank of the storage vessel, according to embodimentsdescribed herein.

DETAILED DESCRIPTION

The following detailed description is directed to technologies forconditioning fluids that are and will be stored in a storage vessel. Inthe following detailed description, references are made to theaccompanying drawings that form a part hereof, and which are shown byway of illustration, specific embodiments, or examples. Referring now tothe drawings, in which like numerals represent like elements through theseveral figures, a fuel system according to the various embodiments willbe described. As described above, the fuel system may be utilized toprovide power to an underwater vehicle, wherein the fuel system includesa fuel cell and a thermal conditioning module configured to receivestored fuel and to condition the fuel before supplying the fuel to thefuel cell.

FIG. 1 illustrates a fuel system 100 that includes a fuel storage vessel101, a fuel cell 102, a thermal conditioning module 104 and anelectronic controller 114. The electronic controller 114 may be acomputer, a processor, or any other hardware and/or software componentthat is configured to control the various components associated with thefuel system 100. In various embodiments, the electronic controller 114may not be a part of the fuel system 100 but may still be configured tocontrol the various components associated with the fuel system 100.

According to embodiments, the fuel cell 102 may be configured to receivea first fluid, such as gaseous oxygen, as a reactant from the thermalconditioning module 104, and to produce a gaseous second fluid, such asgaseous carbon dioxide as an effluent, which is then supplied to thethermal conditioning module 104. In some embodiments where the ventingof gases may be undesirable, the first fluid may be stored as a liquidin the storage vessel 101. In embodiments, the first fluid may be storedin liquid form and in gas form, such that the gaseous first fluid issupplied from the storage vessel to the thermal conditioning module 104.Further, the gaseous second fluid produced by the fuel cell 102 may beconditioned by the thermal conditioning module 104, such that thegaseous second fluid is converted to a liquid second fluid and stored inthe same or different storage vessel. In various embodiments, the fuelcell 102 utilizes gaseous oxygen and kerosene to generate energy andproduces gaseous carbon dioxide as an effluent. It should be appreciatedthat the kerosene, or any other reactant of the fuel cell 102, may besupplied to the fuel cell 102 from a reactant source (not shown).

The thermal conditioning module 104 may be configured to receive thegaseous first fluid stored in the storage vessel 101 via at least one ofa plurality of fluid exit ports 112, which may route fluids stored inthe storage vessel 101 to the thermal conditioning module 104. Thethermal conditioning module 104 may also condition the gaseous firstfluid as the gaseous first fluid travels through the thermalconditioning module 104, after which the thermal conditioning module 104supplies the conditioned gaseous first fluid to the fuel cell 102. Thefuel cell 102 may receive the conditioned gaseous first fluid from thethermal conditioning module 104 via a passage 106. Upon receiving theconditioned gaseous first fluid, the fuel cell 102 may produce thegaseous second fluid, which is supplied to the thermal conditioningmodule 104 via a passage 108. The thermal conditioning module 104 may beconfigured to condition the gaseous second fluid to the liquid secondfluid as the second fluid passes through the thermal conditioning module104. Upon conditioning the gaseous second fluid to liquid second fluid,the thermal conditioning module 104 may deliver the liquid second fluidto the storage vessel 101 via a plurality of fluid entry ports 110. Theliquid second fluid is then stored in a location of the storage vesselfrom where the first fluid is not being supplied. Further detailsregarding the thermal conditioning module 104 will be described inregard to FIGS. 5-8.

The passage 106 may be configured to supply the conditioned gaseousfirst fluid from the thermal conditioning module 104 to the fuel cell102. The passage 108 may be configured to supply the unconditionedgaseous second fluid from the fuel cell 102 to the thermal conditioningmodule 104. In addition, the fuel system also includes a plurality offluid entry ports 110 that may be configured to allow fluids to flowfrom the thermal conditioning module to the storage vessel. Similarly,the fuel system also includes a plurality of fluid exit ports 112 thatmay be configured to allow fluids to flow from the storage vessel to thethermal conditioning module. Details regarding the plurality of fluidentry ports 110 and the fluid exit ports 112 will be described in regardto FIGS. 2-4.

Referring now to FIGS. 2-4, details regarding the storage vessel 101 areshown. FIG. 2 illustrates the storage vessel 101 that includes storagetanks 202, 204, 206 and a storage compartment 208 that is positionedadjacent to one end of the storage tanks 202, 204, 206. It should beappreciated that the storage vessel 101 may include any number ofstorage tanks and any number of storage compartments within the storagevessel 101. In one embodiment, the storage vessel 101 may not includeany storage compartments. In embodiments where there is more than onestorage compartment, the storage compartments may also be arrangedconcentrically or in any other fashion. The storage compartment may belocated anywhere within the storage vessel 101, and may store the sameor different fluid as the storage tanks 202, 204, 206.

In the present embodiment, the storage vessel 101 includes the firststorage tank 202, the second storage tank 204 and the third storage tank206 concentrically arranged such that the first storage tank 202 issurrounding the second storage tank 204, and the second storage tank 204is surrounding the third storage tank 206. The first storage tank 202may include a first fluid entry port 220 and a first fluid exit port222. The second storage tank 204 may include a second fluid entry port224 and a second fluid exit port 226, and the third storage tank 206 mayinclude a third fluid entry port 228 and a third fluid exit port 230. Inaddition, the storage compartment 208 may also include a compartmentfluid entry port 232 and a compartment fluid exit port 234. Theplurality of fluid entry ports 110 (shown in FIG. 1) may include atleast the first fluid entry port 220, the second fluid entry port 224,the third fluid entry port 228, and the compartment fluid entry port232. The plurality of fluid entry ports 112 (shown in FIG. 1) mayinclude at least the first fluid exit port 222, the second fluid exitport 226, the third fluid exit port 230, and the compartment fluid exitport 234. Details of the plurality of fluid entry ports 110 and theplurality of fluid exit ports 112 will be described in detail below inregard to FIG. 3.

In various embodiments, the third storage tank 206 may be nested insidethe second storage tank 204, which may be nested inside the firststorage tank 202. Each of the first, second, and third storage tanks202, 204, 206 have a bottom end, which is adjacent the storagecompartment 208. In some embodiments, each of the three storage tanks202, 204, 206 and the storage compartment 208 may contain the samevolume of fluid or may contain different volumes of fluid.

According to various embodiments, the storage vessel 101 may store onefluid or more than one fluid. In some embodiments, the first storagetank 202 may store a first fluid, the second storage tank 204 may storea second fluid, and the third storage tank 206 may store a third fluid.Further, the storage compartment 208 may be used to store the same or adifferent fluid as the storage tanks. In some embodiments, the threestorage tanks 202, 204, 206 and the storage compartment 208 are sealed,such that the fluid from one of the storage tanks 202, 204, 206 and thestorage compartment 208 may not flow into another storage tank 202, 204,206 or the storage compartment 208.

In the present embodiment, as described above, the storage vessel 101may be utilized for storing liquid oxygen and liquid carbon dioxide.Because of the very low boiling points of these liquids, it is importantthat the storage tanks 202, 204, 206 that store these liquids maintainlow temperatures, such that the liquids do not boil off to gas andthereby increase the pressure inside these tanks 202, 204, 206.Therefore, it may be desirable to protect the storage tanks 202, 204,206 from external environmental conditions by covering them withinsulating materials and/or a vacuum gap. The vacuum gap may be a gapbetween two storage tanks that is a vacuum. The vacuum gap may serve asan insulator, such that the amount of heat exchange between the twostorage tanks is reduced.

The external environmental conditions for a particular storage tank mayinclude conditions that exist outside that particular storage tank.Specifically, these external environmental conditions may includeenvironmental conditions, such as the temperature, pressure, andillumination of the environment around the storage tanks. In someembodiments, the storage vessel may be used to store cryogenic liquids,such as liquid oxygen, which has a boiling point of around −290° F. andliquid carbon dioxide, which has a boiling point of around −60° F.Therefore, if the storage vessel 101 is placed in normal environmentalconditions, for example, at 45° F., the temperature inside the storagevessel 101 is significantly lower than the environmental conditionsexternal to the storage vessel 101. Further, because the storage tanks202, 204, 206 are concentrically arranged, the external conditions ofthe first storage tank 202 may be influenced by the externalenvironmental conditions, such as the temperature outside the storagevessel 101 on one side, and by the temperature inside the second storagetank 204. It should be appreciated that the conditions external to aparticular storage tank 202, 204, 206 or storage compartment 208 mayinfluence the conditions inside the storage tank or storage compartment.

According to embodiments, the storage vessel 101 may utilize insulatingmaterial such as a multi-layer insulation in a vacuum gap, evacuatedpowder insulation or foam insulation, to protect the storage vessel 101from external environmental conditions. Each storage tank 202, 204, 206may be surrounded by an insulating material to protect each storage tank202, 204, 206 from external environmental conditions that exist in theremaining storage tanks 202, 204, 206 and storage compartment 208. Insome embodiments where space is limited, it may be desirable to utilizea smaller amount of space for insulating the storage tanks. Therefore,the insulating material may be a thin layer of multi-layer insulation,which surrounds each of the storage tanks 202, 204, 206. In variousembodiments, the bottom end of the storage tanks 202, 204, 206 is alsosurrounded by insulating material, such that the conditions present inthe storage compartment 208 may not affect the fluid in the storagetanks 202, 204, 206. By insulating the storage tanks 202, 204, 206, thefluid stored in the storage tanks 202, 204, 206 may be protected fromconditions that may be present in the remaining storage tanks 202, 204,206.

In one embodiment, each storage tank 202, 204, 206 may be surrounded bya vacuum jacket, which serves as an insulator for the storage tank itsurrounds. Similar to the vacuum gap, the vacuum jacket may surround astorage tank such that a vacuum surrounds the storage tank, which servesas an thermal insulator to reduce the amount of heat exchange betweenthe storage tank and the external environment surrounding the storagetank.

According to embodiments, the first storage tank 202 may be surroundedby a first insulating material 210, which may be configured to protectthe first storage tank 202 and the contents inside the first storagetank 206 from the external environmental conditions that may influencethe conditions, such as the temperature, inside the first storage tank202. Similarly, the second storage tank 204 may be surrounded by asecond insulating material 212, which may be configured to protect thesecond storage tank 204 and the contents inside the second storage tank204 from the external environmental conditions exposed to the surface ofthe second storage tank 204 that is in contact with the secondinsulating material 212, such as the environmental conditions inside thefirst storage tank 202. It should be appreciated that the secondinsulating material 212 may also protect the first storage tank 202 fromthe environmental conditions present in the second storage tank 204. Thethird storage tank 206 may be surrounded by a third insulating material214, which may be configured to protect the third storage tank 206 andthe contents inside the third storage tank 206 from the externalenvironmental conditions exposed to the surface of the third storagetank 204 that is in contact with the third insulating material 214. Itshould further be appreciated that the third insulating material 214 mayalso protect the second storage tank 204 from the environmentalconditions present in the third storage tank 206. Hence, the insulatingmaterial may protect each storage tank from the external environmentalconditions that surround that particular storage tank. As a result, anychange in environmental conditions, such as a change in temperature thatoccurs in a particular storage tank may be isolated to that particularstorage tank.

The insulating material may be any type of insulation known to thoseskilled in the art. Because the storage tanks may store cryogenicliquids, the insulating material should be able to insulate the storagetanks even at very low temperatures. In one embodiment, vacuum jacketsmay surround the storage tanks. A vacuum jacket may include multi-layerinsulation, powder insulation, or foam insulation within the jacket,which serves as an insulator.

In order to maintain the pressure inside the storage vessel 101, and theindividual storage tanks 202, 204, 206 and the storage compartment 208,a seal 236 may be placed at the top end of the storage vessel 101. Thoseskilled in the art may appreciate that the seal 236 may allow the fluidentry ports 220, 224, 228, 232 and fluid exit ports 222, 226, 230, 234of the three storage tanks 202, 204, 206 and storage compartment 208 topass through the seal 236, such that there is no leakage present betweenthe fluid entry ports 220, 224, 228, 232 and fluid exit ports 222, 226,230, 234 and the seal 236. It should be appreciated that the seal 236may be made from a variety of materials that are known to those skilledin the art. It may be desirable to select a seal that may operate underthe conditions in which the storage vessel will be utilized. Forinstance, in embodiments where the storage vessel 101 is being used tostore liquid oxygen, a seal that is capable of operating under extremelycold temperatures may be used. Further details regarding the seal 236will be described below in regard to FIG. 3.

Referring now to FIG. 3, the storage vessel 101 may include fluid entryports 220, 224, 228, 232 and fluid exit ports 222, 226, 230, 234. Invarious embodiments, fluid entry ports 220, 224, 228, 232 and fluid exitports 222, 226, 230, 234 extend out of the storage vessel 101 at the topend of the storage vessel 101, where they may be attached to the thermalconditioning module 104 or a fluid source.

According to embodiments, the first storage tank 202 may include thefirst fluid entry port 220, which may be used to supply fluid from thethermal conditioning module 104 to be stored in the first storage tank202. The first storage tank 202 may also include the first fluid exitport 222, which may be configured to route the stored fluid from thefirst storage tank 202 to the thermal conditioning module 104.

Similarly, the second storage tank 204 may include the second fluidentry port 224, which may be used to supply fluid from the thermalconditioning module 104 to be stored in the second storage tank 204. Thesecond storage tank 204 may also include the second fluid exit port 226,which may be configured to route the stored fluid from the secondstorage tank 226 to the thermal conditioning module 104. In addition,the third storage tank 206 may also include the third fluid entry port228, which may be used to supply fluid from the thermal conditioningmodule 104 to be stored in the third storage tank 206. The third storagetank 206 may also include the third fluid exit port 230, which may routethe stored fluid from the third storage tank 206 to the thermalconditioning module 104.

In various embodiments, the compartment fluid entry port 232 may extendfrom outside the storage vessel 101, pass through the inner most storagetank, and into the storage compartment 208. In some embodiments, theinner most storage tank may be the third storage tank 206. Thecompartment fluid entry port 232 may be used to supply a fluid from thethermal conditioning module 104 to the storage compartment 208. Further,the storage vessel 101 may include the compartment fluid exit port 234,which similar to the compartment fluid entry port 232, may extend fromoutside the storage vessel 101, and pass through the inner most storagetank to the storage compartment 208. In various embodiments, the fluidpassing through the compartment fluid entry port 232 and compartmentfluid exit port 234 may be affected by the conditions present inside theinner most storage tank. In order to reduce the effects caused by theconditions present inside the inner most storage tank, the compartmentfluid entry port 232 and compartment fluid exit port 234 may besurrounded by insulating material as well.

As described above, the seal 236 may be configured to receive the fluidentry ports 220, 224, 228, 232 and fluid exit ports 222, 226, 230, 234,while also be configured to maintain the pressure inside each of thestorage tanks 202, 204, 206 and the storage compartment 208. The seal236 may include a first seal 237A configured to maintain the pressureinside the first storage tank 202, a second seal 237B configured tomaintain the pressure in the second storage tank 204 and a third seal237C configured to maintain the pressure in the third storage tank 206.

Referring now to FIG. 4, the storage vessel 101 may further include aplurality of sensors 402, 404, 406, 408 that may be configured tomonitor the environmental conditions within various parts of the storagevessel 101. The first sensor 402 may be positioned within the firststorage tank 202, and configured to monitor at least one of thetemperature and pressure inside the first storage tank 202. Similarly,the second sensor 404 may be positioned within the second storage tank204, the third sensor 406 may be positioned within the third storagetank 206, and the compartment sensor 408 may be positioned within thestorage compartment 208 of the storage vessel 101. The second sensor404, the third sensor 406, and the compartment sensor 408 may all beconfigured to monitor at least one of the temperature and pressureinside the second storage tank 204. It should be appreciated that anynumber of sensors may monitor any number of conditions inside each ofthe storage tanks 202, 204, 206 and storage compartment 208 of thestorage vessel 101. Further, although not shown in the drawings, itshould be understood that the sensors may be in direct or indirectcommunication with the electronic controller 114 that is configured tocontrol the operation of the fuel system 100. For the sake of clarity,the fluid entry ports 220, 224, 228, 232 and fluid exit ports 222, 226,230, 234 are marked with dotted lines.

Referring now to FIG. 5, details regarding the thermal conditioningmodule 104 will now be described. It should be appreciated that thethermal conditioning module 104 described herein may be utilized forconditioning fluids in a wide variety of applications. However, for thesake of clarity, the present disclosure will describe the thermalconditioning module 104 as it is utilized within the fuel system 100that utilizes gaseous oxygen as a reactant, and produces gaseous carbondioxide as an effluent. The thermal conditioning module 104 may beconfigured to receive and condition gaseous oxygen, such that it is in asuitable condition for being supplied to the fuel cell 102. Further, thethermal conditioning module 104 may also be configured to receive andcondition gaseous carbon dioxide such that it is in a suitable conditionfor being stored in the storage vessel.

According to embodiments, the thermal conditioning module 104 mayinclude a first storage tank entry valve 510, configured to control theflow of the oxygen from the thermal conditioning module 104 to the firststorage tank 202 via the first fluid entry port 220. A first storagetank exit valve 512 may be configured to control the flow of oxygen fromthe first storage tank 202 to the thermal conditioning module 104 viathe first fluid exit port 222. Similarly, the thermal conditioningmodule 104 may also include a second storage tank entry valve 514,configured to control the flow of the oxygen from the thermalconditioning module 104 to the second storage tank 204 via the secondfluid entry port 224. A second storage tank exit valve 516 may beconfigured to control the flow of oxygen from the second storage tank204 to the thermal conditioning module 104 via the second fluid exitport 226. The thermal conditioning module 104 may also include a thirdstorage tank entry valve 518, configured to control the flow of theoxygen from the thermal conditioning module 104 to the third storagetank 206 via the third fluid entry port 228. A third storage tank exitvalve 520 may be configured to control the flow of oxygen from the thirdstorage tank 206 to the thermal conditioning module 104 via the thirdfluid exit port 230. In addition, the thermal conditioning module 104may also include a storage compartment entry valve 522 configured tocontrol the flow of fluids to the storage compartment 208 via thecompartment fluid entry port 232 (shown in FIG. 4) and a storagecompartment exit valve 508 configured to control the flow of fluids fromthe storage compartment to the thermal conditioning module 104 via thecompartment fluid exit port 234 (shown in FIG. 4).

The thermal conditioning module 104 may also include other valves, suchas a first effluent valve 524, a second effluent valve 526, a firstrecycling valve 528 and a second recycling valve 530. The first effluentvalve 524 may be configured to control the flow of the effluent from thefuel cell 102 into the first storage tank 202 of the storage vessel 101.When the first effluent valve 524 is open, the effluent is able to flowinto the first storage tank. Similarly, the second effluent valve 526may be configured to control the flow of the effluent from the fuel cell102 into the second storage tank 204 of the storage vessel 101. When thesecond effluent valve 526 is open, the effluent is able to flow into thesecond storage tank 204. The rate at which the effluent is able to flowinto the first storage tank 202 and the second storage tank 204 may becontrolled by the electronic controller 114, which may be capable ofopening and closing the first effluent valve 524 and second effluentvalve 526, respectively. Further, the first recycling valve 528 may beconfigured to control the flow of fluid flowing through the first fluidexit port 222 back into the first storage tank 202. The second recyclingvalve 530 may be configured to control the flow of fluid flowing throughthe second fluid exit port 226 back into the second storage tank 204.The amount of fluid that may flow through the first recycling valve 228and the second recycling valve 230 may be controlled by the electroniccontroller 114. Details regarding these valves and others are describedbelow.

Further, the thermal conditioning module 104 may also include back-upvalves that may operate in the event of a failure of another valve, andmay also include various check valves, pressure release valves and othertypes of valves that may be utilized to improve the operation of thethermal conditioning module 104. In addition, the thermal conditioningmodule 104 may include a variety of regulators that may be utilized toregulate the flow of fluids to reduce any back pressure buildup and tosupply the fluids at a desired pressure.

It should be appreciated that the valves, regulators, and othercomponents utilized during the operation of the fuel system 100 may becontrolled by the electronic controller 114. Further, the sensorsdescribed above in FIG. 4 and additional sensors positioned throughoutthe fuel system 100 that may monitor various operating conditions, maycommunicate information with the electronic controller 114, which mayprovide the electronic controller 114 with information to make decisionsregarding the operation of the fuel system 100. Further details of theelectronic controller 114 will be described later.

The thermal conditioning module 104 may also include a first heatexchanger 540, a second heat exchanger 542, a compressor 544 and aplurality of heating elements, such as a first heating element 532, asecond heating element 534, and a storage tank heating element 548.Further, the thermal conditioning module 104 may include a boil off fan546 that is electronically controlled by the electronic controller 114.It should be appreciated that the thermal conditioning module 104 mayinclude other parts, components and/or module, such as regulators,valves, and fans that are not shown in FIG. 5. Details regarding theoperation of the components associated with the thermal conditioningmodule 104 will be described in detail along with the operation of thefuel system 100 with regard to FIGS. 6-8.

According to embodiments, the thermal conditioning module 104 utilizesthe heat exchangers 540, 542 to condition the carbon dioxide. Because ofthe temperature difference that exists between the gaseous oxygen andgaseous carbon dioxide, passing the two gases through the heatexchangers 540, 542 allows the gaseous oxygen to absorb the heat of thecarbon dioxide. The gaseous oxygen that enters the storage vessel 101may be slightly higher than −290° F., which is the boiling point ofliquid oxygen. The gaseous carbon dioxide entering the thermalconditioning module 104 from the fuel cell 102 may be at around 60° F.Therefore, due to the large temperature difference between the twogases, efficient heat exchange may take place.

The thermal conditioning module 104 may be configured to efficientlycool down and liquefy the carbon dioxide produced by the fuel cell 102using the gaseous oxygen supplied by the storage tank. Therefore, thegaseous carbon dioxide that enters the thermal conditioning module 104is at 60° F. at 15 psi, and may need to be conditioned, such that thegaseous carbon dioxide is liquefied and stored in the storage vessel atbelow −60° F. at 100 psi. In order to obtain this, the thermalconditioning module 104 receives the gaseous oxygen and passes itthrough the first heat exchanger 540. Some of the gaseous oxygen is thenpassed through to the second heat exchanger 542 before it enters thefuel cell 102.

The gaseous carbon dioxide produced by the fuel cell 102 is initiallysupplied to the second heat exchanger 542 at about 60° F. at 15 psi,where the heat of the gaseous carbon dioxide is absorbed by the gaseousoxygen, thereby cooling the gaseous carbon dioxide to about −60° F. at15 psi. The cooled gaseous carbon dioxide is then supplied to acompressor 544, which compresses the cooled carbon dioxide from 15 psito 100 psi. It may be desirable to compress the carbon dioxide aftercooling it, as it may be more energy efficient to do so. Next, thepressurized carbon dioxide is supplied to the second heat exchanger 542at −60° F. at 100 psi, where it is further cooled and liquefied toliquid carbon dioxide at less than −60° F. As the pressurized carbondioxide passes through the first heat exchanger 540, the gaseous oxygenthat was supplied by the storage vessel 101 absorbs the heat of thepressurized carbon dioxide, hence cooling the carbon dioxide enough toliquefy it to liquid carbon dioxide.

FIGS. 6-8 describe various routines utilized by the fuel system 100during operation. However, before the various routines are performed bythe fuel system 100 during operation, the fuel system 100 performsvarious routines for preparing the fuel system 100 prior to use. Forinstance, the storage vessel 101 may need to be filled with liquidoxygen at a specific temperature and pressure. In one embodiment, theliquid oxygen is stored in all three storage tanks 202, 204, 206. Somegaseous oxygen may be present inside the three storage tanks 202, 204,206 as well. Also, gaseous oxygen is stored in the storage compartment208 at −60° F. and 100 psi, to prevent the liquid carbon dioxide fromfreezing and to reduce any adverse performance issues due to backpressure being generated in the fuel system 100. Further, the valvesthat control the flow of fluid from the storage tanks 202, 204, 206 tothe thermal conditioning module 104 are closed.

Referring now to FIG. 6, a routine 600 for operating the fuel system 100is described. The routine 600 begins at operation 602, where the fuelcell 102 is initiated. As the fuel cell 102 is initiated at operation602, the routine 600 proceeds to operation 604, where the electroniccontroller 114 may open the first storage tank exit valve 512. As thefirst storage tank exit valve 512 is opened, unconditioned gaseousoxygen present in the first storage tank 202 may flow through the firstfluid exit port 222, through the first storage tank exit valve 512, andinto the first heat exchanger 540.

From operation 604, the routine 600 proceeds to operation 606, where theunconditioned gaseous oxygen is supplied to the first heat exchanger540. As described above, the gaseous oxygen absorbs some of the heat ofthe pressurized carbon dioxide that is partially conditioned by thesecond heat exchanger 542 and the compressor 544. As the gaseous oxygenand the pressurized carbon dioxide pass through the first heat exchanger540, the unconditioned gaseous oxygen is warmed by absorbing the heat ofthe pressurized carbon dioxide. From operation 606, the routine 600proceeds to split to operation 608, and operation 612.

At operation 608, a portion of the warmed oxygen is supplied to at leastone boil off fan, such as the boil off fan 546. At operation 608, someof the warmed gaseous oxygen is routed back towards the storage vessel101. In the present embodiment, the warmed gaseous oxygen is routed backto the storage tank 101 that is supplying the gaseous oxygen to thethermal conditioning module, which according to the present embodiment,is the first storage tank 202. The boil off fan 546 may be utilized tobuild a pressure difference, such that some of the warmed gaseous oxygencoming out of the first heat exchanger 540 is rerouted back to the firststorage tank 202.

From operation 608, the routine 600 proceeds to operation 610, where thewarmed gaseous oxygen is routed through the storage tank heating element548, such that the warmed gaseous oxygen may be warmed further beforeentering the first storage tank 202. The conditioned gaseous oxygen maythen pass through at least one of the storage tank fluid entry valves510, 514, 518. The fuel system 100 may determine the storage tank fromwhich to receive the gaseous oxygen, and may therefore open the valveassociated with the fluid entry port of that particular storage tank. Asdescribed above, the first storage tank 202 is being used to supply theoxygen and therefore, the electronic controller 114 may open the firststorage tank fluid entry valve 510, allowing the conditioned gaseousoxygen from the storage tank heating element 548 to be routed back tothe first storage tank 202, where the conditioned gaseous oxygen maybubble through the liquid oxygen stored in the first storage tank 202.

It may be appreciated that the boil off fan 546 may operate at a fixedspeed to generate a fixed flow rate or may be operated at a higher orlower speed to either increase or decrease the flow rate of gaseousoxygen being routed to the first storage tank, respectively. It shouldbe appreciated that depending upon the amount of power demanded, theelectronic controller 114 may vary the speed of the one boil off fan 546accordingly. For instance, when the fuel cell 102 needs to produce morepower, the electronic controller 114 may increase the speed of the boiloff fan speed 546, thereby routing more gaseous oxygen through the boiloff fan 546 and thus, more gaseous oxygen through the first storage tank202, and eventually to the fuel cell 102 via the conditioning processdescribed herein.

From operation 606, the routine 600 also proceeds to operation 612,where the remaining warmed gaseous oxygen that passed through the firstheat exchanger 540 may be received by the second heat exchanger 542. Asdescribed above, the remaining warmed gaseous oxygen is furtherconditioned by absorbing heat from the unconditioned carbon dioxidesupplied by the fuel cell 102 that also passes through the second heatexchanger 542.

From operation 612, the routine 600 proceeds to operation 614, where theconditioned remaining gaseous oxygen is supplied to the fuel cell 102.It may be appreciated that the conditioned gaseous oxygen passes througha pressure regulator (not shown) prior to being supplied to the fuelcell 102 via passage 106. The pressure regulator may reduce the pressureat which the conditioned remaining gaseous oxygen is being supplied tothe fuel cell 102. The routine 600 continues to operate until theelectronic controller 114 determines that the first storage tank 202 isnot supplying enough gaseous oxygen for the desired functioning of thefuel cell 102.

Referring now to FIG. 7, a routine 700 for conditioning the gaseouscarbon dioxide produced by the fuel cell 102 is described. The routine700 begins at operation 702, where the thermal conditioning module 104receives the unconditioned gaseous carbon dioxide from the fuel cell 102via passage 108. From operation 702, the routine 700 proceeds tooperation 704, where the unconditioned carbon dioxide received from thefuel cell 102 is cooled by passing the unconditioned carbon dioxidethrough the second heat exchanger 542. As described above, cooler oxygensupplied from the first heat exchanger 540 passes through the secondheat exchanger 542 as well, and absorbs some of the heat of theunconditioned carbon dioxide.

From operation 704, the routine 700 proceeds to operation 706, where thecooled gaseous carbon dioxide is pressurized by passing the cooledcarbon dioxide through the compressor 544. From operation 706, theroutine 700 proceeds to operation 708, where the pressurized carbondioxide then passes through the first heat exchanger 540, where thepressurized carbon dioxide is converted to liquid carbon dioxide. Asdescribed above, the unconditioned gaseous oxygen supplied from at leastone of the storage tanks 202, 204, 206 absorbs the heat of thepressurized carbon dioxide as it passes through the first heat exchanger540, liquefying the carbon dioxide.

From operation 708, the routine proceeds to operation 710, where theelectronic controller 114 determines where the liquefied carbon dioxideis to be stored. Initially, the electronic controller 114 may open thecompartment fluid entry valve 522 to store the liquefied carbon dioxidein the storage compartment 208. However, once the storage compartment208 is filled with the liquefied carbon dioxide and the thermalconditioning module 104 has conditioned the first storage tank 202, suchthat the first storage tank 202 may store the liquefied carbon dioxide,the electronic controller 114 may close the compartment fluid entryvalve 522 and open the first storage tank fluid entry valve 510.

From operation 710, the routine 700 proceeds to operation 712, where theliquid carbon dioxide is routed to the desired storage location of thestorage vessel 101. In the present embodiment, the desired storagelocation of the storage vessel is the location whose fluid entry valveis open. In various embodiments, once the first storage tank is alsofilled with liquid carbon dioxide, the electronic controller 114 mayclose the first storage tank fluid entry valve 510 and open the secondstorage tank fluid entry valve 514, such that the liquefied carbondioxide may be stored in the second storage tank 204. From operation712, the routine 700 proceeds to operation 714, where the pressure ofthe carbon dioxide tank being filled is controlled to a safe pressure byrelieving the pressure periodically and venting the oxygen (and carbondioxide) gases in the tank through the storage compartment exit valve508, the first storage tank exit valve 512, or the second storage tankexit valve 516 to the stream entering the first heat exchanger 540.

Referring now to FIG. 8, a routine 800 for receiving gaseous oxygen fromthe second storage tank 204 after the first storage tank 202 is notsupplying enough gaseous oxygen to the fuel cell 102 and conditioningthe first storage tank 202 for storing liquid carbon dioxide isdescribed. The routine 800 begins at operation 802, where the thermalconditioning module 104 is routing unconditioned gaseous oxygen from thefirst storage tank to the first heat exchanger 540 via the first fluidexit port valve 512. From operation 802, the routine 800 proceeds tooperation 804, where the electronic controller 114 determines that thefirst storage tank 202 is not supplying enough gaseous oxygen. Theelectronic controller 114 utilizes the first sensor 402, amongst othercomponents to gather information such as the remaining liquid oxygenvolume to determine if more gaseous oxygen can be supplied by the firststorage tank 202. Upon determining that the first storage tank 202cannot supply enough gaseous oxygen, the electronic controller 114 mayopen the second storage tank fluid exit valve 516. Depending upon howmuch gaseous oxygen is being supplied by the first storage tank 202, theelectronic controller 114 may controllably open the second storage tankfluid exit valve 516 of the second storage tank 204 to provide enoughgaseous oxygen from the second storage tank 204 to make up thedifference between the gaseous oxygen supply demanded by the fuel cell102 and that being supplied by the first storage tank 202. As the firststorage tank 202 supplies less unconditioned gaseous oxygen, theelectronic controller 114 may gradually open the second storage tankfluid exit valve 516 further, thereby increasing the flow rate of theunconditioned gaseous oxygen being supplied from the second storage tank204.

From operation 804, the routine 800 proceeds to operation 806, where theelectronic controller 114 may close the first storage tank fluid exitport valve 512 and open the first reconditioning valve 528. By doing so,the gaseous oxygen within the first storage tank 202 may now circulatethrough the first storage tank 202. The gaseous oxygen may leave thefirst storage tank 202 through the first fluid exit port 222, the firstreconditioning valve 528, the first heating element 532, the first fluidentry port 510, and circulate back into the first storage tank 202. Thefirst heating element 532 may be configured to heat the gaseous oxygenas it circulates around the storage tank, thereby supplying heat to thefirst storage tank 202. It should be appreciated that the amount of heatsupplied by the first heating element 532 may be controlled by theelectronic controller 114, such that if the temperature in the firststorage tank 202 needs to be quickly increased, the first heatingelement 532 may operate at a higher heat level. As the gaseous oxygen isbeing heated during the cycle, the temperature of the first storage tank202 is increasing. The conditioning process may continue until the firststorage tank 202 is ready to receive liquid carbon dioxide. Uponcompletely conditioning the first storage tank, the first reconditioningvalve 428 may be closed. It may be appreciated that the first storagetank is conditioned to a prespecified temperature such that the firststorage tank is in condition to receive the liquid effluent. In variousembodiments, the prespecified temperature should be greater than themelting point of the effluent and less than the boiling point of theeffluent such that the effluent does not freeze or boil inside theconditioned first storage tank.

From operation 806, the routine 800 proceeds to operation 808, where thewarmed gaseous oxygen from the second storage tank 204 is passed throughthe first heat exchanger 540. From operation 808, the routine 800 splitsand proceeds to operation 810 and operation 812. At operation 810, thewarmed gaseous oxygen from the second storage tank 204 is rerouted backto the storage vessel 101 via the boil off fans. As described above, thewarmed gaseous oxygen is rerouted back to the second storage tank 204,causing the second storage tank 204 to supply more gaseous oxygen to thefirst heat exchanger 540.

From operation 808, the routine 800 also proceeds to operation 812,where the remaining warmed gaseous oxygen is further conditioned bypassing the warmed gaseous oxygen through the second heat exchanger 542,similar to operation 612, as described above. The routine 800 thenproceeds to operation 814, where the conditioned gaseous oxygen issupplied to the fuel cell 102. Finally, the routine 800 then proceeds tooperation 816, where the gaseous carbon dioxide is conditioned andsupplied to the storage vessel 101. Details of how the gaseous carbondioxide produced from the fuel cell 102 is conditioned to liquid carbondioxide stored in the storage vessel has been described above in FIG. 7.From operation 816, the routine 800 then proceeds to operation 818,where the liquid carbon dioxide is stored in the conditioned firststorage tank 202. In various embodiments, the electronic controller 114may determine that the storage compartment 208 is full via the sensorpositioned within the storage compartment 208. Upon determining that thestorage compartment 208 is full, the electronic controller 114 may closethe compartment fluid entry port valve 522 and open the first storagetank fluid entry valve 510, rerouting the liquid carbon dioxide to theconditioned first storage tank 202. The routine 800 then ends.

It should be appreciated that the size of the storage vessel 101 and thesize of the respective storage tanks 202, 204, 206 and storagecompartments 208 are designed according to the particular applicationthey are utilized for. For instance, in the present embodiment, the fuelsystem 100 may be configured to accommodate enough liquid carbon dioxideproduced by the fuel cell 102 from the time the fuel cell 102 isinitiated up to the time the first storage tank 202 no longer containsenough liquid oxygen to supply to the fuel cell 102 and the time ittakes for the fuel system 102 to condition the first storage tank 202,such that it may be able to store the liquid carbon dioxide.Additionally, the storage compartment 208 may be configured to store aprespecified amount of the liquid carbon dioxide even after the thermalconditioning module begins to receive the gaseous oxygen from the secondstorage tank 204. The prespecified amount of carbon dioxide may be theamount of carbon dioxide produced by the fuel cell 102 from the time thefirst storage tank 202 begins to start supplying gaseous oxygen to thethermal condition module 104 up to the time the first storage tank 202stops supplying gaseous oxygen to the thermal conditioning module 104,and the amount of carbon dioxide produced by the fuel cell 102 from thetime the second storage tank 204 starts supplying gaseous oxygen to thethermal conditioning module 104 up to the time the first storage tank202 is conditioned and ready to store liquid carbon dioxide.

According to various embodiments, the mass, volume and density of thestorage vessel 101 may be an important consideration during theconstruction and application of the storage vessel 101. For instance, ina fuel system for an underwater vehicle, the density of the fuel systemand its individual components may be a consideration for maintaining thebuoyancy of the vehicle. In such embodiments, the mass of the fluidbeing stored in the storage tanks 202, 204, 206, the mass of the emptystorage vessel 101, and the mass of the fluid being stored in thestorage compartment 208 may all be relevant in determining the mass anddimensions of the storage vessel 101. In addition, the material used,the thickness of insulation, and the thickness of the walls of thestorage tanks 202, 204, 206 may be considerations that may be taken intoaccount before construction of the storage vessel 101 begins.

It should be appreciated that that the present disclosure is not limitedto a fuel system 102, but to any technology that may be utilized forconditioning fluids. Further, those skilled in the art will appreciatethat the scope of the present disclosure includes, but is not limited toapplications for conditioning a first fluid by absorbing the heat of asecond fluid, wherein the second fluid has a higher boiling point thanthe first fluid.

The subject matter described above is provided by way of illustrationonly and should not be construed as limiting. Various modifications andchanges may be made to the subject matter described herein withoutfollowing the example embodiments and applications illustrated anddescribed, and without departing from the true spirit and scope of thepresent invention, which is set forth in the following claims.

What is claimed is:
 1. A fuel system, comprising: a fuel cell; a storagevessel configured to store a first fluid to be supplied to the fuel celland a second fluid supplied by the fuel cell, wherein the first fluidcomprises a liquid first fluid and a gaseous first fluid and wherein thesecond fluid comprises a liquid second fluid and a gaseous second fluid,the first fluid being oxygen and the second fluid being carbon dioxide;and a thermal conditioning module, the thermal conditioning moduleconfigured to receive the gaseous first fluid from the storage vessel,receive the gaseous second fluid from the fuel cell, condition thegaseous first fluid stored in the storage vessel by absorbing heat fromthe gaseous second fluid, such that the fuel cell receives the gaseousfirst fluid from the thermal conditioning module, and convert thegaseous second fluid received from the fuel cell to the liquid secondfluid and storing the liquid second fluid in the storage vessel.
 2. Thefuel system of claim 1, wherein the thermal conditioning modulecomprises a first heat exchanger configured to receive the gaseous firstfluid from the storage vessel and further configured to liquefy thegaseous second fluid into the liquid second fluid by allowing thegaseous first fluid to absorb heat from the gaseous second fluid.
 3. Thefuel system of claim 2, wherein the storage vessel comprises a firststorage tank, a second storage tank, a third storage tank, and a storagecompartment, the first, second, and third storage tanks beingconcentrically arranged with respect to each other so that the thirdstorage tank is nested inside of the second storage tank and the secondstorage tank is nested inside of the first storage tank, the first,second, and third storage tanks configured to store the liquid firstfluid, and the storage compartment configured to store the liquid secondfluid.
 4. The fuel system of claim 3, wherein the first storage tank andthe second storage tank are configured to store the first fluid and uponremoving the first fluid from the first storage tank, store the secondfluid in the first storage tank.
 5. The fuel system of claim 4, whereinthe second storage tank may be configured to store the second fluid uponremoving the first fluid from the second storage tank.
 6. The fuelsystem of claim 1, wherein the thermal conditioning module may beconfigured to control the flow of the first fluid and the second fluidout of and into the storage vessel using a plurality of valves.
 7. Thefuel system of claim 3, wherein the storage compartment is configured tostore at least a prespecified amount of the second fluid even after thethermal conditioning module begins to receive the first fluid from thesecond storage tank, wherein the prespecified amount of the second fluidcomprises the amount of the second fluid that is produced by the fuelsystem from the time the first storage tank begins to supply the firstfluid to the thermal conditioning module to the time the first storagetank stops supplying the first fluid to the thermal conditioning module,and the amount of the second fluid that is produced by the fuel systemfrom the time the thermal conditioning module begins to receive thefirst fluid from the second storage tank up to the time the firststorage tank is conditioned and ready to store the second fluid.
 8. Afuel system, comprising: a thermal conditioning module configured toreceive a gaseous first fluid from a storage vessel, the first fluidbeing oxygen; receive a gaseous second fluid from a fuel cell, thesecond fluid being carbon dioxide; condition the gaseous first fluidfrom the storage vessel by absorbing heat from the gaseous second fluidto create a conditioned gaseous first fluid; provide a first portion ofthe conditioned gaseous first fluid to the fuel cell; provide a secondportion of the conditioned gaseous first fluid back to the storagevessel; convert the gaseous second fluid received from the fuel cell toa liquid second fluid; and provide the liquid second fluid to thestorage vessel.
 9. The fuel system of claim 8, further comprising: thefuel cell; and the storage vessel configured to store the gaseous firstfluid, the conditioned gaseous first fluid, and the liquid second fluid.10. The fuel system of claim 9, wherein the storage vessel is furtherconfigured to store a liquid first fluid.
 11. The fuel system of claim10, further comprising: an electronic controller communicatively coupledto the thermal conditioning module and operative to remove the liquidfirst fluid from the storage vessel; and upon removing the liquid firstfluid from the storage vessel, condition the storage vessel forreceiving the liquid second fluid.
 12. The fuel system of claim 10,wherein the storage vessel comprises a first storage tank, a secondstorage tank, a third storage tank, and a storage compartment, thefirst, second, and third storage tanks being concentrically arrangedwith respect to each other so that the third storage tank is nestedinside of the second storage tank and the second storage tank is nestedinside of the first storage tank, the first, second, and third storagetanks configured to store the liquid first fluid, and the storagecompartment configured to store the liquid second fluid.
 13. The fuelsystem of claim 12, wherein the second storage tank may be configured tostore the liquid second fluid upon removing the liquid first fluid fromthe second storage tank.
 14. The fuel system of claim 12, wherein thestorage compartment is configured to store at least a prespecifiedamount of the liquid second fluid even after the thermal conditioningmodule begins to receive the gaseous first fluid from the second storagetank, wherein the prespecified amount of the liquid second fluidcomprises the amount of the liquid second fluid that is produced by thefuel system from the time the first storage tank begins to supply thegaseous first fluid to the thermal conditioning module to the time thefirst storage tank stops supplying the gaseous first fluid to thethermal conditioning module, and the amount of the liquid second fluidthat is produced by the fuel system from the time the thermalconditioning module begins to receive the gaseous first fluid from thesecond storage tank up to the time the first storage tank is conditionedand ready to store the liquid second fluid.
 15. The fuel system of claim8, wherein the thermal conditioning module may be configured to controlthe flow of the gaseous first fluid and the liquid second fluid out ofand into the storage vessel using a plurality of valves.
 16. A fuelsystem, comprising: a fuel cell; a storage vessel comprising a firststorage tank and a second storage tank, each configured to store a firstfluid to be supplied to the fuel cell, the first fluid being oxygen, anda storage compartment configured to store a liquid second fluid suppliedby the fuel cell, the second fluid being carbon dioxide; and a thermalconditioning module configured to receive the first fluid from thestorage vessel, receive a gaseous second fluid from the fuel cell,condition the first fluid received from the storage vessel by absorbingheat from the gaseous second fluid received from the fuel cell to createa conditioned first fluid, provide a first portion of the conditionedfirst fluid to the fuel cell from the thermal conditioning module,provide a second portion of the conditioned first fluid back to thestorage vessel, convert the gaseous second fluid received from the fuelcell to the liquid second fluid, and provide the liquid second fluid tothe storage vessel for storage in the storage compartment.
 17. The fuelsystem of claim 16, wherein the first fluid comprises a liquid firstfluid and a gaseous first fluid.
 18. The fuel system of claim 17,wherein the thermal conditioning module comprises a boil off fan,wherein the conditioned first fluid comprises conditioned gaseous firstfluid, and wherein being configured to provide the second portion of theconditioned gaseous first fluid back to the storage vessel comprisesbeing configured to create a pressure differential utilizing the boiloff fan to provide the second portion of the conditioned gaseous firstfluid back to the storage vessel.
 19. The fuel system of claim 18,further comprising an electronic controller operative to vary a speed ofthe boil off fan to control an amount of the second portion of theconditioned gaseous first fluid provided back to the storage vessel. 20.The fuel system of claim 19, wherein the electronic controller isfurther operative to detect that the fuel cell needs to produce morepower, and in response to detecting that the fuel cell needs to producemore power, increasing the speed of the boil off fan to increase theamount of the second portion of the conditioned gaseous first fluidprovided back to the storage vessel.